\begin{tikzpicture}
    \tkzDefPoints{0/0/O}
    \tkzDefPoint(180:1.5){A}
    \tkzDefPoint(0:1.5){B}
    \tkzDefPoint(300:1.5){C}
    \tkzDefLine[perpendicular=through A,normed](O,A)  \tkzGetPoint{e}
    \tkzDefPointOnLine[pos=1.5](A,e)  \tkzGetPoint{E}

    \tkzDrawCircle[thick](O,A)
    \tkzDrawPoint(O)
    \tkzDrawPolygon(A,B,C)
    \tkzDrawLine[add=0 and 1](E,A)
    \tkzMarkAngle[size=.5](A,B,C)
    \tkzMarkAngle[size=.5](E,A,C)
    \tkzLabelPoints[below](O)
    \tkzLabelPoints[left](A)
    \tkzLabelPoints[right](B)
    \tkzLabelPoints[below](C)
    \tkzLabelPoints[left](E)
\end{tikzpicture}

